1. Field of the Invention
The present invention relates to a bearing structure, and more particularly, to a bearing structure and a retainer of a bearing suitable for a device where a plurality of bearings is disposed in line in an axial direction.
This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2009-116902, filed on May 13, 2009, the entire contents of which are incorporated herein by reference.
2. Description of Related Art
A power transmission device where a plurality of bearings is disposed in line in an axial direction is disclosed in JP-A-2007-240003 (FIG. 3).
As shown in FIG. 7, in the power transmission device, a plurality of (two in a disclosed example) eccentric bodies 4 and 6, whose outer peripheries are eccentric with respect to an axis O1 of an input shaft 2, is disposed in line in an axial direction of the input shaft 2. Bearings 8 and 10 are disposed on the outer peripheries of the eccentric bodies 4 and 6, respectively, so as to be arranged in line. External gears 12 and 14 are disposed on the outer peripheries of the bearings 8 and 10, respectively. As the eccentric bodies 4 and 6 are rotated, the (two) external gears 12 and 14 are oscillated with a phase difference of 180°. The external gears mesh with the inner portion of an internal gear (not shown).
The bearings 8 and 10 include needle-like rollers 20 and 22 and retainers 24 and 26, respectively. Both end faces of the needle-like rollers 20 and 22 in the axial direction are pressed by pressing portions 24A, 24B, 26A, and 26B of the retainers 24 and 26, respectively. The adjacent pressing portions 24B and 26A of the pressing portions 24A, 24B, 26A, and 26B come into contact with each other, so that the retainers 24 and 26 are positioned in the axial direction.
However, since the adjacent pressing portions 24B and 26A of the retainers 24 and 26 come into contact with each other in the bearing structure in the related art, the lengths of the needle-like rollers 20 and 22 in the axial direction are decreased by the thicknesses of the pressing portions 24A and 24B or the pressing portions 26A and 26B in the axial direction. As a result, there have been problems in that allowable torque is decreased by as much as the decrease in the thicknesses, the lifespan is shortened, and the support stability also deteriorates.
However, in order to avoid these problems, if the lengths of the needle-like rollers in the axial direction are set to be increased, the length of the entire bearing structure in the axial direction is increased by as much as the increased length. As a result, the length of a device where the bearing structure is assembled is increased in the axial direction.